The RISC-V Supervisor Binary Interface (SBI) allows supervisor-mode
software to be portable across all RISC-V implementations by defining
an abstraction for platform (or hypervisor) specific functionality.
See https://github.com/riscv/riscv-sbi-doc/blob/master/riscv-sbi.adoc
for more information.

OpenSBI provides an open-source reference implementation of the RISC-V
SBI specifications which can be easily extended by RISC-V platform and
system-on-chip vendors to fit a particular hardware configuration.